1. Field of the Invention
The present invention relates to a belt steering unit employed for a printer and, more particularly, to a belt steering apparatus for controlling inclined movement of a belt capable of being circulated by at least two rollers.
2. Description of the Related Art
Referring to FIG. 1 which shows a typical electrophotographic printer, a resetting apparatus 15, laser scanning units 16, developing apparatuses 17, a drying apparatus 18 and a transfer apparatus 20, are adjacent to the circulation path of a photosensitive belt 14 circulated by three rollers 11, 12 and 13, and are arranged in a predetermined space.
In the printing process, each laser scanning unit 16 scans laser beams over the photosensitive belt 14 circulating via the resetting apparatus 15. An electrostatic latent image is formed on the photosensitive belt 14 by the scanned laser, and the electrostatic latent image is developed by a developer supplied by the developing apparatus 17. A color image is formed on the photosensitive belt 14 by the laser scanning units 16 scanning laser beams having different color information and the developing apparatuses 17 developing the scanned color information image with developing materials corresponding thereto. The color image formed on the photosensitive belt 14 by the developing material is first transferred to a transfer roller 21 rotating in contact with the photosensitive belt 14, via the drying apparatus 18, according to movement of the photosensitive belt 14. Then, the image is transferred from the transfer roller 21 onto a sheet of paper 23 which moves forward between the transfer roller 21 and the pressure roller 22.
Meanwhile, the photosensitive belt 14 must be kept on a constant path during the above printing. Referring to FIG. 2 which shows a conventional belt steering apparatus for controlling the path of the photosensitive belt 14, a roller 13 is installed on a first frame 30. The first frame 30 is hinged at hinge H to a second frame 40 connected to a main body (not shown). Rotary shafts 13a of the roller 13 pass through grooves 31 and 32 at the sides of the first frame 30 and are retained by plates P, P'.
A circular plate type cam member 35 is connected to the rotary shaft 34 of a motor 33 installed on one side of the first frame 30. One of the rotary shafts 13a of the roller 13 is fitted into a curved groove 36 of the cam member 35 having a radius which varies at a predetermined rate. Thus, the rotary shaft 13a of the roller 13 is raised and lowered by rotation of the motor 33.
The support structure of the cam member 35 and the motor 33 for raising and lowering the roller 13 with respect to the first frame 30 cannot withstand the pressure of the photosensitive belt 14 on the roller 13. In the support structure, when the roller 13 is moved to tighten the photosensitive belt 14, the pressure of the photosensitive belt 14 against the roller 13 is increased. Thus, the expansion range of the photosensitive belt 14 is limited.